Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

444
FXUS63 KLOT 200628
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
128 AM CDT Sat Jun 20 2026

.KEY MESSAGES...

- A period of showers is expected this evening into the
  overnight hours. A stray thunderstorm or two and locally
  gusty winds will be possible in the evening (20% chance).

- There is the potential for heavy rain and thunderstorms in the
  region on Sunday, though if and where a flooding threat will
  materialize here locally remains uncertain.

&&

.DISCUSSION...
Issued at 315 PM CDT Fri Jun 19 2026

Through Saturday night:

Mostly sunny skies amidst broad surface high pressure has
allowed temperatures to warm into the low to mid 70s this
afternoon. Expect temperatures to warm another 2-3 degrees with
highs generally in the mid to upper 70s this afternoon. A lake
breeze hugs the shoreline in Illinois which should hold
temperatures in the upper 60s to around 70.

A cluster of thunderstorms have developed upstream across
northern Minnesota in the vicinity of a weak disturbance diving
across the Upper Midwest. The expectation is that any shower and
storm activity associated with this feature will remain largely
north of the area. However, a separate area of showers and
isolated thunderstorms is ongoing across northern Iowa that is
tied to a separate sheared out vort and along a low to mid level
frontal axis. This activity will continue to slide east
southeast toward the area this afternoon. 18Z DVN RAOB shows a
layer of marginal instability (MUCAPE of ~550 J/kg) in place to
our west. While instability is expected to decrease with
eastward extent and with time, lapse rates may be just steep
enough here locally to support lightning strikes persisting
into at least portions of the area this evening. Have
accordingly maintained a 15-20% chance for thunderstorms as the
showers move across the area but again this should be very
isolated. Given dewpoints have dropped into the upper 40s to
lower 60s, the larger dewpoint depressions may support locally
stronger gusts being brought down to the surface, potentially as
high as 35-45 mph with the tallest showers/storms.

Showers end from north to south through the night with perhaps a
few light showers or sprinkles lingering well south of I-80
after daybreak. Saturday will be similar to today, perhaps with
just slightly warmer temperatures (upper 70s to around 80)
inland with an afternoon lake breeze again keeping temperatures
cooler near the lakeshore.

Petr


Sunday:

The most notable upper-level disturbance progged to track
through our region over the next seven days will eject eastward
out of the central Rockies on Saturday and reach our neck of
the woods on Sunday, accompanied by an attendant surface low.
Ensemble guidance over the past few days has struggled to get a
good handle on how this ejecting shortwave disturbance and
associated surface low will evolve, and this theme has continued
with the latest ensemble suite. The existing and persisting
ensemble variance can partly be explained by slight differences
in the configuration of various influencing synoptic-scale
features this weekend, but it is also a likely byproduct of the
extensive coverage of convection that is expected across the
central Plains on Saturday and what effects that may have in
modulating the main synoptic wave and surface low. Because of
the role that this central Plains convection may play in
dictating the strength and track of the shortwave and surface
low, their ultimate evolution will likely not be truly known
until Saturday night at the earliest, once observational trends
with the Plains convection have become apparent (and even then,
there`s no guarantee that the system`s track and strength will
become obvious). Despite the existing uncertainties, there is
fair agreement across the ensemble suite that this system will
track over or close enough to our area for at least part, and
quite possibly all, of our CWA to see rain from it on Sunday, so
made no changes to the 70-90% PoPs delivered by the NBM.

Model guidance generally favors precipitable water values
peaking anywhere between 1.25" and 2" here, which raises concern
for notable rainfall rates that could bring about some
potential for flooding. Whether such a threat for flooding will
ultimately materialize here, though, appears to be contingent
upon either 1.) a relatively strong surface low developing and
tracking across or just south of our forecast area and inducing
a robust deformation band on its northern flank that steadily
pumps out rainfall at a good clip as it persists over the same
areas for a few hours, and/or 2.) the surface low tracking far
enough to the north for the associated warm front, richer
boundary layer moisture (70+ degree dew points), and greater
instability to enter our forecast area, allowing for
convectively-driven torrential rainfall rates to occur with any
thunderstorms that develop near and south of the front. Will
also note that the latter scenario would also introduce a
potential for severe weather for at least our southern counties
on Sunday. The envelope of the latest ensemble and deterministic
forecast guidance shows mixed support for both of these
scenarios, but there are also several advertised outcomes with
relatively weak surface lows and more southerly surface low
tracks that would make this a relative non-event for our area
with fairly insignificant rainfall totals and little to no
thunderstorm activity north of I-74. The bottom line right now
though is that, while a great deal of uncertainty remains,
Sunday continues to be a day to monitor for potential weather
impacts in our area, so stay tuned for forecast updates.

Monday through Thursday:

After the Sunday system clears the region, quieter and drier
conditions should settle into the area for the beginning of the
upcoming work week. However, there remains a signal for another
upper-level disturbance embedded within northwesterly flow aloft
to bring another round of precipitation to the area sometime in
the late Tuesday through Wednesday time frame. Global ensemble
meteograms are otherwise in relatively good alignment on
temperatures remaining near to below normal for this time of
year through at least the middle of the upcoming week.

Ogorek

&&

.AVIATION /06Z TAFS THROUGH 12Z SUNDAY/...
Issued at 1225 AM CDT Sat Jun 20 2026

Key Messages:

- VCTS through 0730Z, mainly at MDW and GYY.

- Breezy westerly winds (gusts 20-25 kt) develop later this
  morning and continue into the afternoon.

- Lake breeze wind shift likely by early (late) this evening
  (afternoon) at MDW/ORD (GYY).

Some scattered showers and thunderstorms recently developed
along the I-80 corridor in northern IL. This activity is
shifting to the east-southeast and will be in the vicinities of
MDW and very near GYY through 0730Z, before this activity shifts
out of the area.

While there are otherwise no significant aviation weather
concerns anticipated through the period, breezy westerly winds
(gusts 20-25 kt) will develop later this morning into this
afternoon. Then, as the winds begin to abate into early this
evening, a lake breeze is likely to shift the winds onshore at
ORD, MDW and GYY around, or just before sunset. Wind speeds
should ease quickly following the easterly wind shift, with
winds likely going light (under 5 kt) and variable by mid to
late evening as a surface ridge axis shifts overhead.

KJB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.

&&

$$

Visit us at weather.gov/chicago